In the past, various different types of electrical circuits were utilized for controlling the operation of a refrigerant compressor in an automotive type air conditioning system. For instance, some of the past electrical circuits had a control device with a snap acting switch operable therein in response to a preselected high fluid pressure of refrigerant generally at a suction side of the compressor in the system to selectively energize a coil of a clutch device thereby to couple it in driving relation with the compressor in the system. When so driven or turned "on", the compressor was operable to compress vaporized refrigerant discharging it at a high fluid pressure and temperature into the system toward a condenser. Upon passing through the condenser, the vaporized refrigerant was, of course, condensed back to its liquid state at the high fluid pressure and temperature thereof, and from the condenser, the liquid refrigerant was orificed or passed through an expansion valve or tube. Of course, upon this orificing or expansion of the hot, high fluid pressure liquid refrigerant through the expansion valve, the refrigerant experienced a pressure and temperature drop and again changed state back to a cooler low fluid pressure vapor, and in this cooler, low fluid pressure vaporized state, the refrigerant was passed through an evaporator and back to the suction side of the compressor. When the refrigerant fluid pressure on the suction side of the compressor attained a preselected low value, the snap acting switch in the control device was operable in response thereto to effect the deenergization of the clutch device coil thereby to uncouple the clutch device from its driving relation with the compressor interrupting its operation in the system, i.e., turning "off" the compressor. Of course, the fluid pressure of the vaporized refrigerant on the suction side of the compressor was subjected to atmospheric temperature so as to be a direct function thereof, and when the fluid pressure of such vaporized refrigerant was increased in response to the atmospheric temperature to the preselected high value thereof, the control device effected the reenergization of the electrical circuit to reinitiate the operation or cycle of the compressor in the system in the same manner discussed hereinbefore.
Assuming that the windshield and other windows of an automotive vehicle employing the above discussed past air conditioning system may have accumulated some moisture or frost thereon, it was convenient to operate such past air conditioning system in order to effect the evaporation or defrost of such accumulated moisture or frost, as is well known to the art. However, if the atmospheric temperature was low, say for instance about 40.degree. F. or less, it is believed that the fluid pressure of the refrigerant generally at the suction side of the compressor subjected to this low atmospheric temperature was maintained thereby at a value less than the preselected high value necessary to effect the operation of the snap acting switch of the control device, and as a result, the past electrical circuits may not have been energized to effect the operation of the compressor in the past air conditioning systems. This inability of the past electrical circuits and associated past air conditioning systems to remove or otherwise evaporate the accumulated moisture or frost from the inside of the vehicle windshield and other windows is believed to be one of the disadvantageous or undesirable features of such past electrical circuits for controlling such past air conditioning systems.